New York|Travelers to Dominican Republic Lead New York City in Positive Zika Tests

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Travelers to Dominican Republic Lead New York City in Positive Zika Tests

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Pediatrics 2000, a clinic in Harlem where many of the patients have roots in the Dominican Republic, is working to educate patients about the risks of the Zika virus.CreditCreditJoshua Bright for The New York Times

More than half of those who have tested positive for the Zika virus in New York City had traveled in recent months to the Dominican Republic, the city’s health department said on Wednesday, releasing data from its latest round of testing.

The results were a stark reminder that, as the summer travel season begins, many of the most popular destinations for New Yorkers in the Caribbean and Latin America pose a serious health risk, especially for pregnant women.

The new and more detailed data — which broke down cases by borough and by travel history — was issued in a health alert to doctors and health care providers across the city.

Dr. Mary T. Bassett, the city’s health commissioner, said that of the 233 people who have tested positive, 140 had reported recently arriving from the Dominican Republic.

After the Dominican Republic, the places most frequently visited by patients who tested positive for the virus were Puerto Rico, with 20 cases, and Guyana, the small South American nation, with 14.

Dr. Bassett said the results should not be used to stigmatize any group, but to raise awareness. “It won’t serve New Yorkers well if we create the impression that Zika is a Dominican problem or a Puerto Rico problem or a Guyana problem,” she said.

A vast majority of people who contract the virus, spread most commonly by mosquitoes, have no symptoms, and those who do become sick generally experience only mild illness. Pregnant women, however, face a different set of dangers.

Zika poses the greatest risk to a developing fetus, and has been linked to a number of birth defects, including microcephaly, a condition that causes children to be born with abnormally small heads and brain damage.

Various studies have found the risk that a baby will have microcephaly to be 1 percent to 29 percent.

In rare cases, the virus has been associated with Guillain-Barré syndrome, a disorder in which the body’s immune system attacks part of the peripheral nervous system, which can lead to paralysis, usually temporary. In New York City, two people who tested positive for Zika had Guillain-Barré. They have both since recovered, Dr. Bassett said.

There is also a growing concern about the risk of sexual transmission. While all the cases in the city are believed to be travel-related, at least two other cases in New York State are thought to be the result of sexual transmission, health officials said.

Under guidelines issued in February, all women who are pregnant or trying to become pregnant and who have also traveled to Zika-affected countries should be tested, even those with no symptoms.

Several explanations have been offered for why such a large percentage of positive tests involve travel to the Dominican Republic, health officials said.

In recent years, Dominicans have overtaken Puerto Ricans as the largest Latino community in the city, with 747,473 Dominicans living in the five boroughs in 2013, compared with 719,444 Puerto Ricans, according to the most recent census data.

And as recent immigrants, Dominicans have a greater inclination to travel between their home country and New York than other immigrant groups do.

Dr. Bassett said that the numbers might also reflect better access to care, or information, in the Dominican community.

The city separated positive cases by borough for the first time. From Jan. 19 to June 24, 3,906 people were tested. Of the 233 who were found to have Zika, 95 were residents of the Bronx, 52 of Manhattan, 47 of Queens and 39 of Brooklyn.

Of these, 162 were female and 24 were pregnant at the time of the diagnosis. The patients ranged in age from 1 to 74, with a median age of 40.

As the summer travel season picks up, health officials fully expect the number of cases to increase, especially as the virus continues to spread swiftly in South America and the Caribbean.

There are hundreds of pregnant women with Zika in the Dominican Republic, and with each week hundreds of new cases are discovered. In Puerto Rico, the situation is just as dire.

“In the coming months, it’s possible that thousands of pregnant women in Puerto Rico could become infected,” Dr. Tom Frieden, director of the Centers for Disease Control and Prevention, said during a conference call in June.

A version of this article appears in print on , Section A, Page 22 of the New York edition with the headline: Travelers to Dominican Republic Lead New York City in Positive Zika Tests. Order Reprints | Today’s Paper | Subscribe